This invention relates to a communication system for the transmission of closed circuit television signals over an ordinary pair of wires which can also handle the transmission of audio and/or other data over the same wires.
The normal mode of closed circuit television transmission normally involves microwave or a shielded coaxial cable between the camera and the monitor of the television system. This type of closed circuit link may present problems where the installation, for example, is within a building of from one building to another. Such installations may prove both expensive and impractical, not so much, necessarily, because of the cost of the wire in linking up an installation within a building, but because of the time and labor required in running new coaxial cable in an established building or location. Many such applications, for example within a building, already contain miles of unused or spare pairs of wire within the walls and/or floors. Systems have been proposed which connect onto these wires for the transmission of closed circuit television pictures. Such systems, which for many applications are eonomical when compared with installing lengths of shielded coaxial cable, still suffer the disadvantage of time-consuming installation and adjustment requirements. The proposed systems are generally single-ended. When drift occurs in such single-ended systems, the systems are difficult to keep balanced, and require continual readjustments.